Using non-carbon anodes in aluminium electrowinning cells should drastically improve the aluminium production process by reducing pollution and the cost of aluminium production. Many attempts have been made to use oxide anodes, cermet anodes and metal-based anodes for aluminium production, however they were never adopted by the aluminium industry.
U.S. Pat. Nos. 6,248,227 and 6,436,274 (both de Nora/Duruz) disclose a non-carbon, metal-based slow-consumable anode of a cell for the electrowinning of aluminium that self-forms during normal electrolysis an electrochemically-active oxide-based surface layer. The rate of formation of this layer is maintained substantially equal to its rate of dissolution at the surface layer/electrolyte interface thereby maintaining its thickness substantially constant.
A different approach was taken in WO 00/06802 (Duruz/de Nora/Crottaz) where anodes comprising a transition metal-based oxide active surface of iron oxide, cobalt oxide, nickel oxide or combinations thereof, were kept dimensionally stable during electrolysis by continuously or intermittently feeding to the electrolyte a sufficient amount of alumina and transition metal species that are present as oxides at the anode surface.
WO 00/40783 (de Nora/Duruz) further describes the use of HSLA steel with a coherent and adherent oxide surface as an anode for aluminium electrowinning.
Nickel-iron alloy anodes with various additives are further described in WO 00/06803 (Duruz/de Nora/Crottaz), WO 00/006804 (Crottaz/Duruz), WO 01/42534 (de Nora/Duruz), WO 01/42535, (Duruz/de Nora), WO 01/42536 (Duruz/Nguyen/de Nora) and WO02/083991 (Nguyen/de Nora).